[TLS]: Fix #23792.

What happens here is the following:

When using chunked encoding, the ChunkStream sometimes mixes async and sync requests
on the underlying stream.  The async calls work great - just the sync ones create
problems.

In this particular bug, the server returns two ApplicationData records - one big one
and then a smaller one.  The chunk parser requests a sync read of 1024 bytes which
then result in a series of sync reads on the underlying network stream.  The first
two or three network reads don't return enough data to fill the huge ApplicationData
record - the last one then returns so much data that it fills both the remainder of
the first record and the entire second one.

If the caller issued a second sync read, then the implementation would catch this -
but the async code path does not.

mcs/class/Mono.Security/Mono.Security.Protocol.Tls/SslStreamBase.cs

@@ -601,6 +601,9 @@ private void InternalBeginRead(InternalAsyncResult asyncResult)
 				{
 					asyncResult.SetComplete(preReadSize);
 				}
+				else if (recordStream.Position < recordStream.Length) {
+					InternalReadCallback_inner (asyncResult, recbuf, new object[] { recbuf, asyncResult }, false, 0);
+				}
 				else if (!this.context.ReceivedConnectionEnd)
 				{
 					// this will read data from the network until we have (at least) one
@@ -650,6 +653,24 @@ private void InternalReadCallback(IAsyncResult result)
 					return;
 				}
 
+				InternalReadCallback_inner(internalResult, recbuf, state, true, n);
+			}
+			catch (Exception ex)
+			{
+				internalResult.SetComplete(ex);
+			}
+
+		}
+
+		// read encrypted data until we have enough to decrypt (at least) one
+		// record and return are the records (may be more than one) we have
+		private void InternalReadCallback_inner(InternalAsyncResult internalResult, byte[] recbuf, object[] state, bool didRead, int n)
+		{
+			if (this.disposed)
+				return;
+
+			try
+			{
 				bool dataToReturn = false;
 				long pos = recordStream.Position;
 
@@ -713,7 +734,7 @@ record = this.protocol.ReceiveRecord(recordStream);
 						pos = 0;
 				}
 
-				if (!dataToReturn && (n > 0))
+				if (!dataToReturn && (!didRead || (n > 0)))
 				{
 					if (context.ReceivedConnectionEnd) {
 						internalResult.SetComplete (0);
@@ -744,7 +765,6 @@ record = this.protocol.ReceiveRecord(recordStream);
 			{
 				internalResult.SetComplete(ex);
 			}
-
 		}
 
 		private void InternalBeginWrite(InternalAsyncResult asyncResult)
@@ -1022,6 +1042,7 @@ record = null;
 
 							if (remainder > 0) {
 								recordStream.Write (outofrecord, 0, outofrecord.Length);
+								recordStream.Position = 0;
 							}
 
 							if (dataToReturn) {